Electrical resistor



Nov. 19, 1963 M. E. GOODWIN ETAL ELECTRICAL RESISTOR Filed June 7, 1960 INVENTORS MAN/RED 5. 6000147 BY ALEXEV IVKLUDOV ATTORNEY United States Patent cc 3,111,642 ELEQTRKCAL RESISTUR Manfred E. Goodwin, Haddoniield, N32, and Alexey Neiriudov, liroomall, Pa, assignors to International Resistance Company, Philadelphia, Pa.

Filed June 7, 1960, Ser. No. 34,414 2 Claims. (Cl. 338-457) The present invention relates to an electrical resistor, and more particularly to an electrical resistor having an improved insulating jacket of a plastic material.

Many electrical components, such as resistors, require a protective coating of an electrical insulating material, such as a plastic. The protective coating mechanically protects the component from being damaged, and electrically insulates the active element of the component from other components in the electrical circuit in which the component is .used. The electrical properties of many electrical components, prticularly resistors, are often adversely aiiected when the component is exposed to the atmosphere, and particularly when exposed to the moisture in the atmosphere. Therefore, the protective coating should serve. the additional purpose of protecting the active element of the component from the atmosphere, and particularly the moisture in the atmosphere.

A common method heretofore used for applying a protective coating of an insulating plastic around an electrical component is to coat the component with :a liquid plastic either by spraying, painting or dipping, and then curing the plastic layer. However, it has been found that such a protective coating is not sufiiciently impervious to the atmosphere to provide the desired protection, particularly when the component is operating at high temperatures. This was ctound to be true even when the component was provided with a multiple number of coatings of the plastic. In addition, it has been found that such coatings often do not provide the desired electrical insulation since the relatively thin coatings may break down electrically when a load is applied to the component.

Another method of applying a protective plastic jacket around an electrical component is to mold the jacket around the component either by compression or injection molding techniques. It has been found that such a molded protective jacket provides greater electrical insulation for the component as well as better protection against moisture and other contaminants in the atmosphere which may adversely aifect the properties of the component. However, the molded protective jacket which will provide such improved protection is much thicker than the coating of the liquid plastic, and thereby substantially increases the physical size of the component. The modern trend in the electronic field is toward miniaturization of electronic equipment and the components used in such equipment. Therefore, the increase in size provided by the molded protective jacket makes such a protection undesirable.

It is an object of the present invention to provide a novel electrical resistor.

It is another object of the present invention to provide an electrical resistor having an improved insulating jacket of a plastic material.

t is a further object of the present invention to provide an electrical resistor having a protective plastic jacket which is relatively thin but which will protect the resistor from moisture and other contaminants in the atmosphere.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in the drawing a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

3,1 1 1,642 Patented Nov. 19, 1963 The drawing is a sectional View of the resistor of the present invention.

In general, the process of the present invention comprises forming an atmosphere of a pulverulent solid coating plastic, and inserting a heated article into the atmosphere of the coating plastic. The article to be coated is heated to a temperature such that when the article is inserted in the atmosphere of the coating plastic, the particles of the coating plastic which contact the article will fuse to the article, and thereby coat the article. The article is maintained in the atmosphere of the coating plastic until a coating of the desired thickness is obtained. When the article is removed from the atmosphere of the coating plastic, the article may be heated again to insure complete fusion of all of the plastic coated on the article, and the plastic coating is then cured. Although the atmosphere of the pulverulent coating plastic may be formed in a number of different manners, the preferred method of the present invention for forming the atmosphere of the coating plastic is to provide a relatively dense shower of the plastic particles. The articles to be coated are then passed through the shower of the plastic particles, and the articles may be rotated or otherwise placed in motion to insure complete coverage of the article with the coating plastic. Although articles can be coated with a thermoplastic resin by the process of the present invention, the process of the present invention is preferably used for coating articles with a thermosetting resin. For the coating of electrical components with a protective jacket, it has been found preferable to use for the coating plastic a powdered silicone resin or a co-polymer or mixture of a silicone resin and other resins, such as an epoxy resin.

Referring to the drawing, the resistor of the present invention is generally designated as It Resistor it com.- prises a body 12 of an electrical insulating material, such as a ceramic or a plastic. -A layer 14 of a resistance material, such as carbon, a metal or an alloy of metals, is coated on the outersurface of the body 12. Terminal wires 16 extend into holes in the ends of the body 12. The terminal wires 16 are mechanically secured to the body 12; and electrically connected to the resistance material 14 by an electrical-1y conductive cement or solder 18. The plastic protective jacket 20 of the present invention covers the resistance material 14 and the body 12.

It has been found that a plastic protective jacket formed by the method of the present invention provides an electrical component with protection against moisture and other contaminants which is as good as, if not better, than the protection provided by a molded plastic jacket. In addition, the protective plastic jacket formed by the method of the present invention which provides such excellent protection is thinner than the molded plastic jacket so that the completed component is smaller in size than a component having a molded plastic jacket. in fact, the protective plastic jacket formed by the method of the present invention is substantially of the same thickness as a protective jacket applied by painting or spraying a liquid plastic onto the component, yet the protective jacket of the present invention provides the component with a protection which is better than that provided by a molded plastic jacket. For example, the cylindrical body portion of one type of electrical resistor having a protective jacket which was painted or sprayed thereon has a diameter of 0.160 inch and a length of 0.575 inch. The same electrical resistor provided with a molded protective jacket has a diameter of 0.270 inch (almost twice the diameter of the painted or sprayed unit) and a length of 0.720 inch. However, the same electrical resistor provided with a plastic protective jacket coated by the method of the present invention has a diameter of 0.170

inch and a length of 0.580 inch, which is substantially the same size as the painted or sprayed unit.

To determine the ability of the protective jacket of the present invention to Withstand moisture penetration, tWo groups of resistorsof the type having a film of carbon coated on a ceramic cylinder Were subjected to a very strict moisture permeability test. One group of the resistors had a protective jacket of the present invention, and the other group of the resistors had a thicker type molded jacket. it Was found from the results of this test that the protective plastic jacket of the present invention, with regard to preventing moisture penetration, was as good as and in some cases better than the thicker types of protective plastic jackets. Therefore, the plastic protective jacket formed by the method of the present invention does not substantially increase the size of the electrical component, yet provides a protection against moisture which is at least as good as the thicker types of. plastic protective jackets.

The present invention may be embodied in other specific forms vvithout departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

We claim:

1. An electrical resistor comprising a body of an electrical insulation material, a resistance material on said body, terminal Wires extending from said body and electrically connected to said resistance material, and a plas- 4 tic jacket covering said body and the resistance material, said plastic jacket being formed by heating the body portion and inserting the heated body portion in an atmosphere or solid particles of the plastic so as to fuse a continuous layer of said plastic over the entire surface of the body portion.

2. An electrical resistor comprising a body or" an electrical insulation material, a resistance material on said body, terminal Wires extending from said body and electrically connected to said resistance material, and a plastic jacket covering said body and the resistance material, said plastic jacket being formed by heating the body portion and passing the heated body portion through a shower of solid particles of the plastic so as to fuse a continuous layer of said plastic over the entire surface of the body portion.

References Cited in the file of this patent UNITED STATES PATENTS 2,385,702 Hediger et al. Sept. 25, 1945 2,559,077 Johnson et al. July 3, 1951 2,576,942 Jakob Dec. 4, 1951 2,808,351 Colbert et a l. Oct. 1, 1957 2,854,946 Norris Oct. 7, 1958 2,885,310 Olson et al. May 5, 1959 2,885,522 Major et al. May 5, 1959 2,913,357 Ostrofsky et al. Nov. 17, 1959 3,016,875 Ballentine et al. Jan. 6, 1962 3,019,126 Bartholomew Ian. 30, 1962 

1. AN ELECTRICAL RESISTOR COMPRISING A BODY OF AN ELECTRICAL INSULATION MATERIAL, A RESISTANCE MATERIAL ON SAID BODY, TERMINAL WIRES EXTENDING FROM SAID BODY AND ELECTRICALLY CONNECTED TO SAID RESISTANCE MATERIAL, AND A PLASTIC JACKET COVERING SAID BODY AND THE RESISTANCE MATERIAL, SAID PLASTIC JACKET BEING FORMED BY HEATING THE BODY PORTION AND INSERTING THE HEATED BODY PORTION IN AN ATMOSPHERE OF SOLID PARTICLES OF THE PLASTIC SO AS TO FUSE A CONTINUOUS LAYER OF SAID PLASTIC OVER THE ENTIRE SURFACE OF THE BODY PORTION. 